The present invention relates to electrical testing equipment, and more specifically to an electrical testing device which combines voltage sensing functions with voltage metering and continuity functions.
In electrical installations such as those found in manufacturing facilities, large buildings, and even residential housing, electrical wiring related to a number of electrical functions and applications is often bundled together or threaded through a single conduit. The wiring is often confined to small, poorly lit areas of a building, both for aesthetic and practical reasons. Such installations serve an aesthetic purpose in maintaining unsightly wires behind panels or other covering devices. From a practical standpoint, such installations maintain wiring off of floors, thereby decreasing the possibility of accidental damage to the wiring and preventing accidental intervention between people or equipment and electrical wiring.
While maintaining wiring in confined areas makes a great deal of practical sense, such installations can cause significant problems for electricians, technicians, and maintenance personnel faced with the need to troubleshoot electrical wiring problems. For example, when one of a number of conductors in a given installation fails to operate correctly, electrical testing personnel are faced with the problem of quickly determining which of a number of possible conductors has failed. Although conductors are often marked, the markings can be difficult to detect when a number of conductors are bundled together, or when lighting conditions are poor, as is frequently the case in electrical installations. Therefore, the act of locating an appropriate conductor for testing can be a daunting task. Once the appropriate conductor or conductors have been found, additional testing is often required to locate a fault or to verify appropriate operation of a device. A number of tests may be required, including continuity checks to verify the integrity of conductors, AC voltage measurements, and DC voltage measurements. Therefore, a number of electrical tests must be conducted to correct a typical electrical fault.
Although electrical troubleshooting of the type described above can be done using a typical voltage testing device, such as an analog or digital multimeter or voltage tester capable of measuring AC and DC voltages, all of these devices suffer from a number of disadvantages. All of these devices, for example, require the connection of two leads to a conductive point of a circuit to verify a voltage. The electrician must identify both a positive (hot) and negative (neutral) lead, and either locate open terminals coupled to the conductors or pierce the insulation of the conductors to measure the voltage on the leads. This procedure is time consuming, particularly when a large number of conductors are involved. Furthermore, measurement procedures with typical meters require the use of both hands, and are therefore particularly difficult when the user is isolating one or more conductors from a bundle. Complicating matters, many testing devices require the user to operate a number of switches or other electrical activation devices to select a type and expected range of a voltage to be tested before a measurement can be taken. When using a meter of this type, an electrician or technician must simultaneously identify and isolate the appropriate connectors from a bundle, maintain a connection between the conductors and the voltage probes, and operate switches on the metering device. Measurements of this type are extremely difficult, and can require the participation of two or more electricians or technicians.
In some applications, testing can be simplified through the initial use of a non-contact sensor. The non-contact sensor includes a conductive element that, when placed near an AC conductor, provides an indication if an AC voltage is impressed on the conductor. The non-contact sensor, therefore, can be used to determine which of a number of conductors is carrying an AC voltage. In a typical testing situation, therefore, an initial test could be conducted to determine which of a number of AC conductors were xe2x80x9chotxe2x80x9d, and a voltage tester or multimeter could then be applied to determine conductivity and/or voltage ranges of the conductors in question. However, to troubleshoot equipment as described, multiple pieces of test equipment are required. Upon isolating a conductor in which a fault has been located, the user must drop the test equipment, and start over with an additional piece of equipment. Again, a substantial amount of time can be lost, merely in re-locating the appropriate conductor for testing.
The present invention is a multi-functional voltage measuring device which provides circuitry for quickly and easily locating and isolating active conductors from among a plurality of conductors, as well as circuitry for detecting a voltage type and magnitude on the conductor.
To find and isolate a conductor for testing, the device provides the capability of quickly and easily detecting the presence of an active conductor. This capability can be provided through non-contact voltage sensing, single probe voltage sensing, or both. The non-contact voltage sensing employs a sensor for detecting the general vicinity of a conductor carrying an AC voltage without the need for electrical contact between the sensor and the conductor. Therefore, AC voltages can be sensed without the need to strip wires or find an open contact point. Single probe voltage sensing allows the user to determine whether a conductor has an AC voltage impressed upon it by electrically coupling a single probe of the voltage measuring device to the conductor. Therefore, the user does not have to find both a xe2x80x9chotxe2x80x9d and a xe2x80x9cneutralxe2x80x9d side of a voltage to determine whether an AC voltage is impressed upon it. Significantly, both non-contact voltage sensing and single probe sensing require the use of only one hand, thereby leaving the other hand free to isolate a conductor from a bundle. Circuitry associated with these functions provides an indication of the presence of an AC voltage, through at least one of a visual display, such as a flashing LED indicator, and an aural signal, such as an alarm. It is not necessary, therefore, for the user to closely monitor a display to locate an active conductor.
Once a conductor carrying an AC voltage is detected, the user can use both probes to determine additional information about the conductor or conductors under test, such as the magnitude, type, and polarity of the voltage carried by the conductor or conductors. When using both probes, the device provides a number of functions automatically, thereby minimizing the need to activate a number of switches, and simplifying operation, particularly for the single user who can devote only two hands to testing. The device preferably automatically determines the type (AC or DC) and polarity of DC voltages under test, and is preferably auto-ranging, providing a visual indication of the range of the voltage being tested without the need to activate switches or other actuating devices. The device can also includes a continuity check circuit, which is also automatically available to the user without the need to select a continuity function. To further reduce the requirement for switches or electrical actuators, the device preferably defaults to a sleep mode, wherein power consumption is minimized until one of a selected number of inputs is received.
A preferred feature of the auto-ranging circuitry is the ability for a single circuit to process both an AC and a DC input voltage and to scale each type of signal appropriately. The circuit includes a resistor and capacitor coupled in series, the capacitor and resistor being electrically coupled to other impedances to provide an impedance divider to AC voltages, while acting as an open circuit to DC voltages. An additional scaling impedance, therefore, is applied to AC voltages, which may have magnitudes as much as two times greater than the magnitude of the applied DC voltages. This circuit minimizes the need for expensive, high-accuracy microprocessors and analog to digital converters, thereby minimizing the cost of the device. Furthermore, the circuit establishes a high impedance connection between the terminals, and therefore allows a batter operated continuity check circuit to be continually connected across the test probes without significant current flow, thereby extending the life of the voltage source powering the continuity check circuit.
These and other objects and advantages of the invention will be apparent from the detailed description and drawings.